Distributed spacecraft formation control method based on communication quantization

Abstract

A communication quantization distributed spacecraft formation control method comprises the following steps: establishing a spacecraft dynamic model near an asteroid, modeling a gravitational field near the asteroid by adopting a polyhedron method, constructing a spacecraft formation near a balance point in the gravitational field, and establishing a relative kinematic model of the spacecraft formation; a logarithm quantizer is constructed to quantify state variables transmitted between spacecrafts, a distributed spacecraft formation controller based on communication quantization is constructed, and finally, the quantized state variables are input into the controller to obtain a spacecraft formation deployment strategy. According to the method, the formation control strategy of the spacecrafts near the asteroid is improved by quantifying the communication information, and the distributed spacecraft formation controller based on communication quantification is constructed, so that the problem that the formation communication frequency and the data transmission rate of the existing formation control method near the asteroid are too harsh is solved.

Description

Technical Field

[0001] The present invention relates to a technology in the field of aerospace, specifically a communication quantization-based distributed spacecraft formation control method. Background Technique

[0002] Spacecraft formation flight refers to the use of multiple spacecraft to cooperate to complete complex tasks. The distributed formation structure helps to establish a system with a certain degree of autonomy and redundancy, while significantly reducing the overall mission cost. However, the communication resources of spacecraft performing long-term asteroid gravitational field measurement tasks are severely restricted. To reduce the demanding requirement of real-time data exchange, improved technologies enable the communication between system individuals to be activated only when the quantization level of information changes by inputting a quantization control strategy, enabling system stability even under conditions of limited bandwidth and low-cost wireless networks. However, the quantization control strategy is currently only applied to the communication between some single individual subsystems and the formation attitude consistency control, and has not been used for distributed formation control. Summary of the Invention

[0003] Aiming at the above deficiencies of the existing technology, the present invention proposes a communication quantization-based distributed spacecraft formation control method, which improves the formation control strategy of spacecraft near asteroids by quantizing communication information and constructs a communication quantization-based distributed spacecraft formation controller to solve the problem that the existing formation control methods near asteroids are too demanding on the formation communication frequency and data transmission rate.

[0004] The present invention is realized through the following technical solutions:

[0005] The present invention relates to a communication quantization-based distributed spacecraft formation control method. After establishing the spacecraft dynamics model near the asteroid and using the polyhedron method to model the gravitational field near the asteroid, constructing a spacecraft formation near the equilibrium point in the gravitational field and establishing its relative kinematic model, a logarithmic quantizer is constructed to quantize the state variables transmitted between spacecraft, a communication quantization-based distributed spacecraft formation controller is constructed, and finally the quantized state variables are input into the controller to obtain the spacecraft formation deployment strategy.

[0006] The spacecraft dynamics model is specifically as follows: Where: ω is the constant angular velocity of an asteroid with an irregular shape but uniform density, is the position vector of the spacecraft, U(r) is the gravitational potential function, and d is the perturbation acceleration caused by the uncertainty of the asteroid gravitational field and solar interference.

[0007] The coordinate system of the spacecraft dynamics model is the asteroid body-fixed coordinate system The origin O of the coordinate system is located at the mass center of the asteroid, The axis is along the direction of the minimum inertia axis of the asteroid, The axis is aligned with the angular momentum vector of the spacecraft, The axes form an orthogonal reference system.

[0008] Modeling the gravitational field near the asteroid specifically involves: Where: G = 6.67428×10 -11 m 3 kg -1 s -2 is the gravitational constant, σ e is the constant bulk density of the asteroid, e ∈ edges and f ∈ faces refer to edges and faces respectively, r e and r f are vectors pointing from the spacecraft to a specific point on a certain edge and a certain face respectively, L e terms and ω f are the integral factors of the space between the spacecraft and the edge or face, E e and E f describe the geometric characteristics of the edge and the face respectively.

[0009] The equilibrium points in the gravitational field refer to: at these points, the gravitational force of the asteroid on the spacecraft is exactly balanced with the centrifugal force of rotation, that is As the ideal positions for formation flight, specifically: Where: is the effective gravitational potential, and the ideal positions for formation flight are:

[0010] The relative kinematic model specifically involves: Where: N is the number of formations composed of spacecraft, r i is the position vector of the i-th spacecraft S i , r0 is the equilibrium point position vector, and S i The relative position vector relative to the equilibrium point is the desired state of the spacecraft S i according to the mission requirements, is the error of the spacecraft S i relative to the desired state, is its state sliding mode vector, and α > 0 is the sliding mode coefficient to be set in engineering. Due to the disturbance d i near the asteroid, which is mainly caused by the uncertainty of the gravitational field and solar perturbation, the upper bound is set Technical effects

[0011] The present invention addresses the problem of formation control for spacecraft near asteroids, taking into account the communication resource consumption during formation shape transformation and maintenance. Based on state quantization technology, a communication quantization-based distributed spacecraft formation control technology is designed. Compared with the prior art, the present invention significantly reduces the communication frequency in the spacecraft formation network and effectively solves the problem of excessive communication energy consumption for micro-spacecraft formations near asteroids. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 is a flowchart of the present invention;

[0013] Figure 2 is a system diagram involved in the present invention;

[0014] Figure 3 is a formation communication topology diagram;

[0015] Figures 4 - 6 is a schematic diagram of the simulation results of the embodiment. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0016] As Figure 2 shown, a communication quantization-based distributed spacecraft formation control system involved in this embodiment includes: an expected formation definition unit, a gravitational field estimation unit, a quantization decoding unit, a controller unit, and a communication quantization unit, where: the expected formation definition unit defines the expected formation and position of the spacecraft according to mission requirements and ground instructions; the gravitational field estimation unit obtains the effective gravitational estimation result of the asteroid at the current position based on the gravitational field modeling result of the polyhedron method according to the current position information; the quantization decoding unit decodes according to the quantization ordinal number transmitted by the adjacent spacecraft to obtain the quantization state information of the adjacent spacecraft; the controller unit calculates based on the expected position output by the expected formation definition unit, the gravitational result output by the gravitational field calculation unit, its own state information, and the quantization state information of the adjacent spacecraft output by the quantization decoding unit to obtain the control force of a single spacecraft; the communication quantization unit quantifies the state variables through a logarithmic quantization function based on the position information of each spacecraft, outputs the quantization ordinal number and determines whether to communicate, and realizes the deployment of the spacecraft formation.

[0017] As Figure 1 shown, a communication quantization-based distributed spacecraft formation control method based on the above system, after establishing a spacecraft dynamics model near the asteroid and using the polyhedron method to model the gravitational field near the asteroid, solves for the equilibrium point in the gravitational field and constructs a spacecraft formation near the equilibrium point and establishes a relative kinematic model of the spacecraft relative to the equilibrium point, and then quantifies the state variables transmitted between the spacecraft according to the quantization decoding unit based on the logarithmic quantizer, and inputs the quantified state variables into the controller unit and the communication quantization unit to finally obtain the spacecraft formation deployment strategy.

[0018] The logarithmic quantization mentioned above refers to: where: the quantization density ∈∈(0,1) is a parameter to be set in the project, and the absolute quantization ordinal number k∈Z + , s (k) = ∈ (1-k) s (0) s (0) >0 is the quantization dead zone, is the sector boundary corresponding to the quantization density ∈. The relative error δ of the logarithmic quantizer satisfies the boundary condition: δs = Q(s) - s, δ∈(-β,β).

[0019] The quantization ordinal number k′ of the logarithmic quantizer described is k′ = ksign(s), and the quantized state is decoded and output based on the quantization ordinal number

[0020] The control force of a single spacecraft where: and are respectively the estimated value of the effective gravitational force of the spacecraft and the estimated value of the effective gravitational force at the equilibrium point. γ>0 is a controller gain parameter to be determined, D is the upper bound of the unknown perturbation, - is the Hadamard division, that is, the elements at the corresponding positions between vectors are divided, is the saturation function substitution sign function used to balance the unknown external perturbation force with an upper bound of D, ζ>0 is the coefficient of the saturation function to be designed, and the global sliding mode variable of the spacecraft state b i >0 is the weight coefficient to be designed, s j is the sliding mode variable of the spacecraft S j The state of, Q(s j ) is the result of its quantized output. In engineering design, b i is the weight for the spacecraft to tend to its own desired position and the formation configuration, that is, the larger b i is, the faster the spacecraft S i will converge to its own desired state; the smaller b i is, the more likely it is to maintain the integrity of the formation configuration.

[0021] As Figure 2 shown, for the spacecraft formation deployment, by continuously exchanging the updated quantization ordinal numbers of the logarithmic quantizer between each spacecraft and its adjacent spacecraft, and each spacecraft decodes the received quantization ordinal numbers of the logarithmic quantizer to obtain the updated quantized state, and then each controller unit calculates according to the desired position output by the desired formation definition unit, the gravitational result output by the gravitational field calculation unit, its own state information, and the quantized state information of the adjacent spacecraft output by the quantization decoding unit, so as to realize the distribution control and formation deployment of the spacecraft.

[0022] After specific simulation experiments, four spacecraft were simulated in Matlab to be deployed around the asteroid 433 Eros, with a volume density of 2.67 kg / m 3 , and a rotation period of 5.27 h. A uniform geometric body composed of 856 vertices and 1708 faces was used to model the gravitational field of Eros. Through the simulation calculation of the above method, the equilibrium point position vector was obtained as r0 = [19.156, -2.65, 0.143] T . Deploy a spacecraft formation near r0, and the formation communication topology diagram is as shown in Figure 2 . The initial position vector is ρ1(0) = [-100, -50, 25] T m, ρ2(0) = [100, -50, 25] T m, ρ3(0) = [100, 50, -25] T m, ρ4(0) = [-100, 50, -25] T m, and the initial velocity vector is The desired position vector is The desired position vector is The desired velocity vector is Assume the external disturbance is Where:

[0023] In this embodiment, the spacecraft formation controller parameters include: controller gain γ = 1.6×10 -3 , disturbance upper bound D = 10 -3 , sliding mode coefficient α = 7.5×10 -3 , weight parameter b = 5, quantization density ∈ = 0.75, quantization dead zone s (0) = 10 -5 , saturation function coefficient ζ = 10 -6 . The experimental period is 1200 seconds.

[0024] The experimental data obtained from the simulation are shown in Table 1. The position error column records the error between the positions of each spacecraft in the spacecraft formation and the desired position during the simulation period, verifying that the designed control technology can make the formation converge to the desired formation within the period. The communication times column and the data transmission column compare the communication times and data transmission of using this technology and using the existing traditional continuous communication technology during the simulation period. Assume that the traditional continuous communication frequency is 2 Hz, and the transmitted data uses double precision, with a size of 4 bytes.

[0025] Table 1

[0026] As shown in Table 1, according to the simulation results, the present invention saves about 72.5% of the communication frequency and 95.5% of the data transmission of the formation, significantly reducing the communication burden and energy consumption of the system. As Figures 4 - 6 shown, the simulation results of the formation position error, velocity error and control input of the spacecraft are shown. As can be seen from the figure, the spacecraft formation can tend to the desired state within a limited time under the condition of communication quantization.

[0027] Compared with the prior art, the present invention significantly reduces the communication requirements and energy consumption of the spaceborne system by compressing the continuous full-state information transmission between spacecraft into discrete quantization ordinals.

[0028] The above specific implementation can be locally adjusted by those skilled in the art in different ways without departing from the principle and purpose of the present invention. The protection scope of the present invention is subject to the claims and is not limited by the above specific implementation. All implementation schemes within its scope are subject to the present invention.

Claims

1. A distributed spacecraft formation control method for communication quantization, characterized in that, A spacecraft dynamics model near an asteroid is established, and the gravitational field near the asteroid is modeled using the polyhedron method. After constructing a spacecraft formation near the equilibrium point in the gravitational field and establishing its relative kinematic model, a pair quantizer is constructed to quantify the state variables transmitted between spacecraft, and a distributed spacecraft formation controller based on communication quantization is constructed. Finally, the quantified state variables are input into the controller to obtain the spacecraft formation deployment strategy.

2. The distributed spacecraft formation control method for communication quantization according to claim 1, wherein The described spacecraft dynamics model is specifically as follows: where ω is the constant angular velocity of an irregularly shaped but uniformly dense asteroid, is the position vector of the spacecraft, U(r) is the gravitational potential function, and d is the perturbation acceleration caused by the uncertainty of the asteroid's gravitational field and solar interference; The coordinate system of the described spacecraft dynamics model is the asteroid body-fixed coordinate system The origin O of the coordinate system is located at the mass center of the asteroid, The x-axis is along the direction of the minimum inertia axis of the asteroid, The y-axis is aligned with the angular momentum vector of the spacecraft, The z-axis forms an orthogonal reference system; The modeling of the gravitational field near the asteroid is specifically as follows: where: G = 6.67428×10 -11 m 3 kg -1 s -2 is the gravitational constant, σ e is the constant bulk density of the asteroid, e ∈ edges and f ∈ faces respectively refer to edges and faces, r e and r f are vectors respectively pointing from the spacecraft to a specific point on a certain edge and a certain face, the L e term and ω f are the integration factors of the space between the spacecraft and the edge or face, E e and E f describe the geometric characteristics of the edge and the face respectively; The equilibrium points in the gravitational field mentioned above refer to the points where the gravitational force of the asteroid acting on the spacecraft is exactly balanced with the centrifugal force of rotation, that is As the ideal positions for formation flight, specifically: Where: For the effective gravitational potential, the ideal positions for formation flight are: The relative kinematic model is specifically as follows: where: N is the number of formations composed of spacecraft, r i is the position vector of the i-th spacecraft S i , r0 is the equilibrium point position vector, and S i is the relative position vector relative to the equilibrium point is the desired state of the spacecraft S i according to mission requirements, is the error of the spacecraft S i relative to the desired state, is its state sliding mode vector, and α > 0 is the sliding mode coefficient to be set in engineering. Since the perturbation d i near the asteroid is mainly caused by the uncertainty of the gravitational field and solar perturbation, the upper bound is set as 3. The distributed spacecraft formation control method for communication quantization according to claim 1, characterized in that The logarithmic quantization mentioned above refers to: where: the quantization density ∈∈(0,1) is a parameter to be set in engineering, and the absolute quantization ordinal k∈Z + , s (k) = ∈ (1-k) s (0) , s (0) >0 is the quantization dead zone, is the sector boundary corresponding to the quantization density ∈. The relative error δ of the logarithmic quantizer satisfies the boundary condition:

4. The communication quantization-based distributed spacecraft formation control method according to claim 3, wherein The described pair quantizer quantizes the ordinal number k′ = k sign(s), and decodes the output quantized state based on the quantized ordinal number 5. The communication quantization-based distributed spacecraft formation control method according to claim 1, characterized in that The control force of the single spacecraft Wherein: and are respectively the estimated value of the effective gravitational force of the spacecraft and the estimated value of the effective gravitational force at the equilibrium point. γ is a controller gain parameter to be determined, D is the upper bound of the unknown disturbance, and / is the Hadamard division, that is, the elements at the corresponding positions of the vectors are divided. is a saturation function substitution sign function used to balance the unknown external perturbation force with an upper bound of D. ζ is the coefficient of the saturation function to be designed, and the global sliding mode variable of the spacecraft state b i is a weight coefficient to be designed, s j is the sliding mode variable of the state of spacecraft S j , and Q(s j ) is the result of its quantization output.

6. A distributed spacecraft formation control system for implementing the method according to any one of claims 1-5, characterized in that, It includes: An expected formation definition unit, a gravitational field estimation unit, a quantization decoding unit, a controller unit, and a communication quantization unit, where: The expected formation definition unit defines the expected formation and position of the spacecraft according to the mission requirements and ground instructions; The gravitational field estimation unit obtains the effective gravitational estimation result of the asteroid at the current position based on the polyhedron method gravitational field modeling result according to the current position information; The quantization decoding unit decodes according to the quantization ordinal number transmitted by the adjacent spacecraft to obtain the quantized state information of the adjacent spacecraft; The controller unit calculates based on the expected position output by the expected formation definition unit, the gravitational result output by the gravitational field calculation unit, its own state information, and the quantized state information of the adjacent spacecraft output by the quantization decoding unit to obtain the control force of a single spacecraft; The communication quantization unit quantifies the state variables through the pair quantization function based on the position information of each spacecraft, outputs the quantization ordinal number, and determines whether to communicate to realize the spacecraft formation deployment.

7. The distributed spacecraft formation control system according to claim 6, characterized in that, For the described spacecraft formation deployment, after each spacecraft continuously exchanges the updated pair quantizer quantization ordinal numbers with its adjacent spacecraft and each spacecraft decodes the received pair quantizer quantization ordinal numbers to obtain the updated quantized state, each controller unit calculates based on the expected position output by the expected formation definition unit, the gravitational result output by the gravitational field calculation unit, its own state information, and the quantized state information of the adjacent spacecraft output by the quantization decoding unit to realize the distributed control and formation deployment of the spacecraft.

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